Modern Experimental Techniques in Ultrafast Atomic …
273
from polyatomic molecules such as ethylene glycol, acetone, and CD 3 OD has been
investigated using pump-probe techniques. The yields of H
+
3 and D
+
3 have been measured as a function of pump-probe delay, and the results are plotted in this figure.
The time-dependent variation of the H
+
3 and D
+
3 yields have been observed. This
information can be used to estimate the lifetime of the precursor ion. Details about
the mechanism of H
+
3 formation from polyatomic molecules in an intense laser field
using the pump-probe technique is available in Ref. [47].
5 Experimental Techniques for Detection and Imaging
the Momentum of Electrons and Ions
The interaction of intense femtosecond pulses with the molecules can be used to
study the ultrafast electron and nuclear dynamics in such a system. The electrons,
ions, and neutral particles are generated during this interaction. It would be possible
to reveal the ongoing processes [48] induced by femtosecond pulses by detecting and
measuring the energy/momentum of the electrons/ions/neutral fragments. Different
electron/ion spectrometers have been developed over the past few decades and used
in ultrafast AMO physics to understand the ultrafast dynamics in atomic and molecular systems. Some of these spectrometers are the Time-Of-Flight Mass Spectrometer
(TOF MS), COLd Target Recoil Ion Momentum Spectrometer (COLTRIMS), and
the Velocity Map Imaging (VMI) spectrometer. The working principle of these spectrometers is discussed in the following subsections.
5.1 Time-of-Flight Mass Spectrometer (TOF MS)
Time-of-flight Mass spectrometry is the technique of detecting ions on the basis of
their mass-to-charge ratio. The time-of-flight (TOF) mass spectrometer works on the
principle of measuring the time-of-flight of ions traveling over a distance of known
length. The schematic diagram of a typical TOF mass spectrometer is shown in
Fig. 17.
The linear TOF mass spectrometer consists of a repeller plate, an extractor plate,
a drift tube, and a detector. The region between the repeller and the extractor plates
is called the interaction region. The separation between these plates and the length
of the drift tube are determined by the Mclaren criteria based on the space focusing
condition and will be discussed later in this section [49]. In 1955, Wiley and McLaren
reported an improved time-of-flight mass spectrometer based on dual electrostatic
fields (extraction (E s ) and acceleration regions (E d )) for guiding the ions to the
detector, and a field-free region known as the drift tube.
This design of the TOF spectrometer is known as the classic Wiley-McLaren TOF
spectrometer. In the absence of the second field region (E d is zero), this spectrometer
273
from polyatomic molecules such as ethylene glycol, acetone, and CD 3 OD has been
investigated using pump-probe techniques. The yields of H
+
3 and D
+
3 have been measured as a function of pump-probe delay, and the results are plotted in this figure.
The time-dependent variation of the H
+
3 and D
+
3 yields have been observed. This
information can be used to estimate the lifetime of the precursor ion. Details about
the mechanism of H
+
3 formation from polyatomic molecules in an intense laser field
using the pump-probe technique is available in Ref. [47].
5 Experimental Techniques for Detection and Imaging
the Momentum of Electrons and Ions
The interaction of intense femtosecond pulses with the molecules can be used to
study the ultrafast electron and nuclear dynamics in such a system. The electrons,
ions, and neutral particles are generated during this interaction. It would be possible
to reveal the ongoing processes [48] induced by femtosecond pulses by detecting and
measuring the energy/momentum of the electrons/ions/neutral fragments. Different
electron/ion spectrometers have been developed over the past few decades and used
in ultrafast AMO physics to understand the ultrafast dynamics in atomic and molecular systems. Some of these spectrometers are the Time-Of-Flight Mass Spectrometer
(TOF MS), COLd Target Recoil Ion Momentum Spectrometer (COLTRIMS), and
the Velocity Map Imaging (VMI) spectrometer. The working principle of these spectrometers is discussed in the following subsections.
5.1 Time-of-Flight Mass Spectrometer (TOF MS)
Time-of-flight Mass spectrometry is the technique of detecting ions on the basis of
their mass-to-charge ratio. The time-of-flight (TOF) mass spectrometer works on the
principle of measuring the time-of-flight of ions traveling over a distance of known
length. The schematic diagram of a typical TOF mass spectrometer is shown in
Fig. 17.
The linear TOF mass spectrometer consists of a repeller plate, an extractor plate,
a drift tube, and a detector. The region between the repeller and the extractor plates
is called the interaction region. The separation between these plates and the length
of the drift tube are determined by the Mclaren criteria based on the space focusing
condition and will be discussed later in this section [49]. In 1955, Wiley and McLaren
reported an improved time-of-flight mass spectrometer based on dual electrostatic
fields (extraction (E s ) and acceleration regions (E d )) for guiding the ions to the
detector, and a field-free region known as the drift tube.
This design of the TOF spectrometer is known as the classic Wiley-McLaren TOF
spectrometer. In the absence of the second field region (E d is zero), this spectrometer